With increasing requirements on environment protection, gas and diesel fueled vehicles are gradually being replaced by electric vehicles or hybrid electric vehicles. Power batteries are very important as the main power source of electric vehicles. The in-vehicle power battery generally comprises a plurality of battery modules connected in parallel and/or in series, needs to output powerful energy to meet a sufficient power output, and requires a high voltage, a large current, an excellent charging rate, and high safety performance.
A short-circuit of the power battery and a long term overloading can cause an abnormal condition of electric vehicles, and then cause an electrification of various metal components of electric vehicles. Thus, a user may come into contact with the high-voltage source, thus causing injury, which could lead to a terrible traffic accident. Moreover, when a maintenance person services electric vehicles, he may be hurt by the high voltage of the power battery. Furthermore, when a serious abnormal condition happens, for example, when an electric vehicle collides with a high-velocity mobile object and causes a short-circuit of the battery, the high voltage and large current in the battery can cause damage, such as a fire, when the battery is not cut off timely. Thus, high safety performance of the power battery is required.